This invention relates to glass compositions and methods of making the same. More particularly, this invention relates to glass having high light transmittance in the visible range and/or fairly neutral color. Such glass compositions are useful, for example, in architectural windows, patterned glass applications, residential windows, furniture, solar cells, and/or automotive windows.
Glass that is fairly neutral or clear in color, and highly transmissive to visible light (e.g., at least 75% transmissive, or even more preferably at least 80% transmissive), is sometimes desirable. One way of achieving such a glass is to use very pure base glass materials (e.g., substantially free of colorants such as iron). However, base materials with a high degree of purity are expensive and thus not always desirable and/or convenient. In other words, for example, the removal of iron from glass raw materials has certain practical and/or economical limits.
As can be appreciated from the above, glass raw materials (e.g., silica, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron. The total amount of iron present is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the from of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The blue-green colorant of ferrous iron (Fe2+; FeO) is of particular concern when seeking to achieve a fairly clear or neutral colored glass, since as a strong colorant it introduces significant color into the glass. Ferrous iron is typically a stronger colorant than ferric iron. Thus, while iron in the ferric state (Fe3+) is also a colorant, it is of less concern when seeking to achieve a glass fairly clear in color.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which enables a glass to have fairly clear color and/or high visible transmission, without having to resort to extremely pure (i.e., free of iron) glass raw materials.
U.S. Pat. No. 6,218,323 discloses a neutral colored high transmission glass which can achieve a visible transmission of at least 89%. In order to achieve these characteristics, the glass of the '323 patent requires a very low total iron (expressed herein as Fe2O3) content of 0.01 to 0.03%, and a standard glass redox (FeO/Fe2O3) of 0.25 to 0.35. However, in some instances it is difficult (e.g., expensive and/or impractical) to achieve such a low total iron content of 0.01 to 0.03%. Thus, it will be appreciated by those skilled in the art that there exists a need for a clear glass composition capable of achieving high visible transmission and relatively neutral color regardless of whether or not the total iron is in the very low 0.01 to 0.03% range.